The present invention relates to heat curable organopolysiloxane compositions which utilize a silicon hydride siloxane fluid, silicon vinyl siloxane fluid and a preformed latent platinum catalyst. More particularly, the present invention relates to preformed latent platinum catalysts resulting from reaction between a zero valent platinum complex and an organic nitrogen compound, such as 2,2'-bipyridine, (BIPY) or diethylazodicarboxylate (DEAD) where the reaction to form the preformed latent platinum catalyst is effected in the substantial absence of a silicone fluid.
Prior to the present invention, as shown by Chalk, U.S. Pat. No. 3,188,299, stable mixtures of organosilicon compositions such as mixtures of an alkenyl polysiloxane and a hydrogen polysiloxane and a platinum (II) catalyst were provided having a nitrogen containing ligand. The Chalk patent discloses that chloroplatinic acid can be modified with a nitrogen containing compound such as BIPY. The use of an aromatic heterocyclic nitrogen compound added separately as an inhibitor to a mixture of platinum catalyst, silicone hydride fluid and silicone vinyl fluid is shown by Brown et al, U.S. Pat. No. 4,374,967. A low temperature silicone gel having a greater work life is obtained.
Additional storage stable one part curable organopolysiloxane compositions are shown by Eckberg, U.S. Pat. No. 4,670,531 which suggests the use of DEAD as a separately added inhibitor, or Janik et al, U.S. Pat. Nos. 4,584,361, 4,791,186, and 4,801,642, where certain aliphatic and cycloaliphatic triamines and alkenyl diamines are described which are utilized separately as inhibitors in combination with platinum catalyst in silicone fluid mixtures, to impart long term storage stability at temperatures of up to 40.degree. C., while allowing such silicone compositions to cure at an enhanced rate at 135.degree. C.
Although improved shelf stability over an extended period of time, and cure times at elevated temperatures have been obtained by using various separately added nitrogen containing inhibitors with platinum catalysts in the preparation of one part heat curable organopolysiloxane compositions, the silicone industry is constantly evaluating platinum catalyzed heat curable, one package silicone compositions to optimize their room temperature shelf stability and their cure time at elevated temperatures. As used hereinafter the term "shelf stability" means accelerated shelf aging conditions at 50.degree. C., while "cure time" means rate of cure at from 120.degree. C. to 150.degree. C.